Phase modulation



May 30, 1939. 3` f USSELMAN 2,160,465

PHASE MODULATION Filed Oct. l5, 1932 5 Sheets-Sheet l 4||||- INVENToR IGEORGE L. 5s AN BY/ :l

May 30, 1939- G. l.. ussLMAN 2,160,465

\ PHASE MODULATION Filed Oct. 15, 1932 5 Sheets-Sheet 2 lljllllllll-IIIIIII=IIILJIIIIIIIIIII ATTORNEY May3o,1939. j Q USSELMAN 2,160,465

PHASE MODULATION Filed Oct. 15, 1932 5 Sheets-Sheet 3 INVENToR *I g gGEORGE LMAN BY M11-44 ATTORNEY May 30,1939. G. L. ussELMAN PHASEMODULATION 5 sheets-sheen:

Filed Oct. l5, 1932 mvENToR GEORGE ELM/AMy BY A TRNEY l May 30, 1939. QI USSELMAN :2,160,465

PHASE MoDULATIoN Filed oct. 15, 1952 5 sheets-sheet 5 IIIIIIIIIIIIIIIIIHA A AAA vvvv llllllJIIIIIIIIIIIIIIIIIIIIIII INVENTOR GEORGE s MAN Y BY vM44 ATTORNEY Patented May 30, 1939 PHASE MODULATION George L. Usselman,Port `leferson, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application October 15, 1932, Serial No. 637,923

4i claims. (o1. 179-171) This invention relates to signalling means andin particular to means whereby the characteristics ofhigh frequencyoscillations other than amplitude are varied in accordance with signals5 to be transmitted.

It has been found that ordinary amplitude modulated high frequencyoscillations in transmission from the sending station to the receivingstation are subject to what is known as fading effects. This is adecided disadvantage since it introduces drop-outs and errors in thesignal. VEven where diversity receivers are used to receive theamplitude modulated signals the effect of fading is of seriousdisadvantage.

I have found that if the high frequency oscillations are modulated inphase or in frequency in accordance with the signal to be transmittedthey are somewhat less subject to the effect of fading than amplitudemodulated waves, assuming like amounts of power are utilized in thetransmission. Phase or frequency modulation is advantageous because itallows the transmitter to operate at full output power, whereas inamplitude modulation it is necessary to reduce the power and operate thetransmitter at about one fourth of the full transmitter power output.

The increased signal strength gained by phase or frequency modulation isa great advantage for reducing fading and for increasing the reliabilityof the service.

In each of my United States applications, Se-

rial No. 623,558, sied Ju1y 2o, 1932, Patent f #2,048,900 dated July 28,1936; Serial No. 616,026, led June 8, 1932, Patent #2,036,165 datedMarch 31, 1936; Serial No. 602,487, filed April 1, 1932,. Patent#2,049,143 dated July 28, 1936; Serial No. 607,932, filed April 28,1932, Patent #2,036,164 dated March 31, 1936, I have shown means forvarying at signal frequency the characteristics other than the amplitudeof a carrier frequency wave. In each of these arrangements the carrierfrequency is impressed through phase shifting means onto the controlgrids of a pair of thermionic tubes which have their anodes connected inparallel to a common tank circuit and their internal impedances variedin phase opposition by the signal wave. In each of these arrangementsthe phase modulator stage comprises two tubes having their inputelectrodes symmetrically connected and energized as indicated above, anda common tank circuit connected in parallel to the anodes of said pairof tubes.

The presentinvention relates to an improved modulating means broadly ofthe type referred toabove,

More in detail, this invention relates to an improved modulating meanswherein a single phase modulator stage is preceded by an amplitudemodulator stage which comprises a pair of tubes having control gridsconnected in circuits and 5 energized at carrier frequency in phase. Inaccordance with the present invention each tube is equipped with its ownseparate tank circuit. Moreover, in the present invention, instead ofphase modulating the energy reaching the grids 1U of these two tubes,the phase shifting means is interposed between the' separate tankcircuits and the control electrode. of the single tube in the followingstage. Here, as in the prior` applications, the internal impedances ofthe pair of tubes 15 are varied in opposite senses` by the modulatingfrequencies. In the present case this results in amplitude modulation ofthe carrier. This modulated energy is then fed by way of phase shiftying elements to the control grid of the single 20 phase modulator tube.

The novel features of my invention have been pointed out-withparticularity in the claims appended hereto. l..

The nature cf my invention and the operation 25 thereof will be bestunderstood from the following detailed description thereof and therefromwhen read in connection with the drawings, throughout which likereference numerals indi- Y cate like parts, and in which: 30

Figure 1 illustrates a specific embodiment of the invention; while,

Figures 2, 3, 4 and 5 illustrate modifications of the arrangement ofFigure 1. y

A specic embodiment of my invention is 35 shown in Figure 1. In thisgure A is a source of constant frequency oscillations, such as a crystalcontrolled oscillator or a long line frequency controlled oscillator.The oscillator A is connected in parallel by way of blocking condensersI 40' and 3 to the control grids 2 and ll of tubes G and I-Irespectively of stage C. The tubes G and H are shown as the screen gridtype, although three element tubes may be used. In the latter caseneutralizing circuits: may be necessary. The 45 anode electrodes 6 and 8of tubes G and H respectively are connected to tank circuits M and Nrespectively. Tank circuit M includes a variable capacity l0 and aninductance Il. The tank circuit N includes a variable capacity I0 andin-5o ductance ll'. The alternating current circuits .for tubes G and H arecompleted by connecting the lower terminals of tank circuits M and N byway of by-passing condensers C1 to the grounded sidev of the circuit l2supplying heating current 65 from the source K to the cathodes of thetubes. The energizing circuits for anodes 6 and 8 are completed by Wayof a lead I3 connecting the terminals of inductances II and I I to thesource K. Tank circuit M is connected through a blocking condenser O toone end of the phase retarding element L. Tank circuit N is connectedthrough a blocking condenser P to one end of the phase advancing elementQ. The other ends of both phase shifting elements are connected togetheras shown and to the grid S of tube I in stage D.

The alternating current input circuit of tube I is completed by way ofradio frequency choking inductance I4 and by-pass condenser I5 connectedbetween the grid S and cathode I6 of tube I. The cathode I6 ismaintained at stable potential by connecting one side thereof to groundG as shown. The desired negative potential may be supplied to the grid Sby way of choke coilv I4 and lead I'I connected with source I8. Thealternating current anode cathode circuit of tube I comprises the anode26, tank circuit R, by-pass condenser ZI, and the grounded side ofcathode I6. The direct current anode cathode circuit of tube I comprisesthe anode 20, the inductance 22 of tank circuit R, a portion of thesource I8, and the cathode I6. Tank circuit R may be tuned to thedesired frequency by a variable capacity 23 connected in parallel withinductance 22, The tube I is of the screen grid type and chargingpotential is supplied to the screen grid electrode 24 by a lead 25connected to a point on source I8. Any radio frequency potentialsappearing on 24 are shunted around source I8 by a by-pass condenser 26.It will be understood that the screen grid tube I may be replaced by athree-electrode tube provided proper precautions are taken to obtainstable operation thereof. It should be understood that sources K and I 8may be of any desirable type, such as, storage batteries, motorgenerator sets, or vacuum tube rectiers.

The tank circuit R, of stage D is connected, by way of a line includingblocking condenser U, to the stage E. Stage E may consist of limitingdevices and either frequency multipliers or amplifiers or both. The laststage is connected by transmission lines V-V to the antenna F.

B represents a source of signal frequency of any nature. The source ofmodulating potentials, B, is connected with the primary winding 30 ofasignal frequency transformer T1. The secondary winding 3| of thistransformer is connected as shown by way of radio frequency inductances32 and 32 to the control grids 2 and 4 of tubes G `and H respectively,as shown. The inductances 32 and 32 may be replaced by resistances ifdesired. In order that radio frequencies appearing in inductances 32 and32' do not reach the modulation frequency transformer T1 and source Bconnected therewith, the lower ends of inductances 32 and 32'V areconnected by way of by-passing condensers 33 and 33 to the grounded leadof the cathode heating circuit I2. The proper biasing potentials areapplied to the control electrodes 2 and 4 by way of the secondarywinding 3| and a lead 34 connecting the midpoint Vthereof to apotentiometer P1 connected in shunt with a portion of direct currentsource K. Charging potentials for the screen grid electrodes 3.6. and36' of tubes G and H are supplied by way of lead 31 connected to a pointon potentiometer resistance P2 shunted across source K. Alternatingcurrent appearing on the grid electrodes 36, 36' is shunted aroundsource K by by-pass condensers 38 and 38 connected as shown.

In operation the oscillator A supplies equal amounts of high frequencyexcitation Voltage to each of the control grids 2 and 4 of tubes G and Hin stage C. If there is no signal frequency being supplied to thecontrol grids 2 and 4 from B by way of T1, this high frequency energywill be amplified equally and, if desired, multiplied in frequency intubes G and I-I and tank circuits M and N respectively. This followsfrom the fact that like potentials are applied to the electrodes of4these two tubes and also to the fact that tank circuits M and N aremade to be of similar characteristics. Furthermore (still assuming nopotentials are supplied from B), since in practice the impedances ofphase retarding element L and phase advancing element Q are of equalmagnitude, the high frequency energy reaching the grid S of tube I instage D, from tank circuit M and from tank circuit N, will be of equalintensity. The energies will have equal phase angles, that is, oneleading and the other lagging, about the average phase position. Theresultant phase of the excitation energy supplied to S from M and N willin this case lie midway between the phase angles of the separateenergies supplied from M and N. Stage D amplifies, or, if it is desired,may be adjusted to multiply the carrier frequency before it istransmitted to stage E. As I have said before, the carrier energy may belimited and multiplied in frequency or amplilied, or both, in stage E.From the last stage,\the carrier energy is transmitted through thetransmission line V-V to antenna F, where it is radiated into space. Y

If we now assume that signal frequency is being sent out from source B,the potentials on the grids 2 and 4 of tubes G and H will be varied atsignal frequency in phase opposition or, in other Words, differentially.supplied equally to the control grids 2 and 4 of tubes G and H from thebattery or source K by way of the midtap of the secondary winding 3| oftransformer T1. The end terminals of this winding carry the biaspotential to the control grids 2 and 4. Now take some instant in thesignal when the grid 2 of tuberG will be swung, say, in 'a positivedirection, while the grid 4 of tube H will be swung an equal amount in anegative direction.

The Vcarrier energy produced in oscillator A is delivered in two equalparts to the grids 2 and 4 of tubes Gand H respectively in stage C. One

protionris amplied in amplifier G and appears in tank circuit M, whilethe other portion is amplified 1 irlY amplier H and appears in tankcircuit N. This amplification isnot constant because the amplifiedenergies in the two amplifiers G and H are differentially modulated inamplitude so that the carrier energies delivered by the two ampliers areof the'same phase angle, but of an amplitude which varies at signalfrequency and which is proportional to the signal intensity. Due to theaction of the modulating transformer T1 this variation in amplitude ismade opposite for each amplifier about an average value. Thisdifferentialr action will increase the power output of tubeG and tankcircuit M, while the power output of tube H and tank circuit N will bedecreased a like amount, or Vice versa. The phase deviation or shiftcaused by L and Q in the two high frequency energies supplied to thegrid S of tube I will Vbe equal but the energies will be of unlikesense, and in this case the power supplied from Steady negative bias istank circuitM through phase retarding element L willbe greater than thepower supplied from tank circuit N through phase advancing element Q.

The carrier energy from the tank circuit M connected with amplifierGnpasses through the phase retarding element L, while the carrier energydelivered by the amplifier H to the tank circuit N passes through thephase advancing element Q. These two differentially modulated carrierenergies are impressed on the grid electrode S of tube I at differentphase angles because of the'action of phase shifting elements L and Q.The impedance of La nd Q should be made equal so that they have equaleffect on the amplitude of the carrier energiesdelivered thereby fromtank circuits M and N to control grid electrode S. Itcan be seen that wenow have two carrier energies of the same frequency present on the gridS of tube I and that these two carrier energies have a constant phasediierence but are of an amplitude which varies differentially about aconstant total amplitude or average. In other words, the total energydelivered to the grid S of tube I is` constant and the phase anglebetween the two parts of this energy is also constant. Each of these twoparts of the total carrier energy is amplified or multiplied in"frequency, or both, in tube I and delivered to the tank circuit R ofthe stage D. Tank circuit R has only one degree of freedom, that is, thecarrier frequency or a desired harmonic of the carrier frequency towhich the tank circuit may be tuned so that there can be but oneoscillating current in the tank circuit R.

Because of the phase difference of the two energies fed into the tankcircuit the phase of the oscillating current in the tank circuit will bedetermined or controlled to a greater extent or made to shift towardthat of the carrier energy having the greater amplitude. The amount ofthe shift will be proportional to the excess energy of one part of thecarrier energy over the other part of they carrier energy. The amount ofshift in phase of the carrier energy is limited by the value of thereactances of the phase shifting elements L and Q, as has beenVexplained before. This results in carrier energy in the tank circuit Rof stage D, which will be of substantially constant amplitude but ofvarying phase angle. The frequency of the variation of thisphase angleis the signal frequency and the degree or amount of phase swing or phasedeviation is substantially proportional to the amplitude of the signal.The amount of phase modulation is also controlled by the values of thephase shifting elements L and Q. If the energy in tank circuits M and Nare linearly amplitude modulated in phase opposition, the phase of theenergy appearing in tank circuit R of stage D will be linearly phasemodulated.

The energy delivered from stage D may be utilized in any desired manner.The energy may be amplified or multiplied in frequency and it may beradiated from the antenna F. When the frequency of the phasemodulatedcarrier is multiplied the angle of phase modulation isincreased in the same ratio.

In some cases it may be desirable to impress the modulating potentialson the internal impedances of tubes G and I-I in a different manner thanthat in which they are impressed on said impedances in Figure 1. Forexample, it may be desirable to apply the signal oscillations from B byway of the secondary winding of transformer T1 to the screen girdelectrodes 36, 3B of tubes shown in Figure 2 of the drawings.

G andH respectively in phase' opposition, as When the modulatingpotentials are applied in phase opposition to the screen grid electrodesof tubes G and H steady positive charging potential for said electrodesis supplied by way of a lead 31'1ccnnectedtoapoint onthe resistance ofpotentiometer P2 as shown. In this novel modulating scheme the desirednegative bias is applied to the control electrodes 2 and 4 of tubes Gand H by way of a lead 34 connecting saidvelectrodes to a point on theresistance of potentiometer P1. The mod ulated transmitter of Figure2-is otherwise the same as the transmitter of Figure 1.

The operation of the arrangement of Figure 2 is similar to the operationof the arrangement of Figure 1. The only difference between the twoarrangements is that in Figure 1 the impedances of the tubes G and Harevaried in opposition at signal frequency by varying the effectivepotential on the control grid electrodes', whereas in the arrangement ofFigure 2 the impedances of tubes Gand I-I are varied in phase oppositionat signal frequency Vby varying the effective charging potential appliedto the screen grid electrodes. In each case the carrier frequencyrelayed in tubes G and H Vis differentially modulated in amplitude atsignal frequency.

In yet other cases it may be desirable to accomplish the amplitudemodulation of the carrier in the stage C by means of modulatingthe'anode potentials. W'hen this method of modulating is desired thearrangement of Figure 3 may be used. In Figure 3 the' proper negativebiasing potentials are supplied to the control grids of tubes G and H bya lead 34 as in Figure 2. Direct current potentials for the screen gridelectrodes of 'tubes G and H are supplied by way of a lead 31,

as in Figure 1. In this arrangement, however,

Vthe modulating potentials from the source B are supplied by Way oftransformer T1 in phase opposition to the `anodes 6 and 8 of tubes G andH respectively. Inthis manner anode modulation in amplitude of thecarrier waves passed by tubes G and H is accomplished in the stage C..In other respects the arrangement shown in Figure 3 operatesthe same asthe arrangement of Figure 1. A repetition of the operationA of thesenovel modulating arrangements in connection with Figure 3 is thoughtunnecessary.

When plate modulation of the amplitude of the carrier in ythe unit C bya more eiiicient method is desired, the arrangement ofjFigure 4. may beused. In this arrangement the'tubes G and H are'of the three-electrodetype. Three-electrode tubesare used in this arrangement because, whenthey amplitude modulation of the carrier is accomplished by varying theanode potential, the 'three-electrode tubes give much greater responsethan that obtainable with the four-electrode tubes of Figure'S. Whenthree-electrode tubes are used the capacity between the anode electrodesand'grid electrodesof the tubes G and' H may be neutralized by platecircuit neutralization. This is accomplished by connecting the lowerterminal of the tapped plate inductances l I and Il to the controlelectrodes 2 and 4 of the tubes G and H respectively by way of variableneutralizing capacities NC and NC respectively. 'Ihe charging potentialfor the anode electrodes 6 and 8 is supplied from the lead I3 connectedto the midpoint of the secondary winding 3l of transformer T1 and byleads vconnecting the ends of the secondary winding 3l of transformer T1to the points tapped tothe inductances Il and v,I l.,I

tov

Vas in the prior arrangement.

The arrangement of Figure 4 is otherwise similar to the arrangement ofFigure 3.

TheY phase modulator of Figure 4 operates the same as the phasemodulator of Figure 1. The

1; high frequency oscillations from A are impressed cophasally in equalamounts onto the control electrodes of G and H respectively. 'I'heseoscillations may be amplified or frequency multiplied, or both, in thetubes G and H, and in particular in the output circuits thereof. Thehigh frequency oscillations, whether amplified, frequency multiplied, orboth, are differentially modulated in amplitude in stage C in accordancewith the signal impressed from source B in phase opposition on the anodeelectrodes of tubes G and H. The carrier energies from M and N, whichare of the same phase but of amplitude which varies at signal frequency,are fed through the phase shifting means L and Q to the controlelectrode S of tube I. 'I'he action of the phase shifted energies from Mand N on the control electrode S of tube I results in the production intank circuit R of energy, the phase of which varies at signal frequency,but the amplitude of which is constant, as has been described in detailhereinbefore in connection with Figure 1. The frequency of the phasemodulation of this energy is directly proportional to the signalfrequency andthe degree of phase shift is proportional to the amplitudeof the signal, except as otherwise modified yby thephase shiftingelements L and Q of stage C. The energy from tank circuit/R is fed byway of coupling unit U to the unit E, from which it may be radiated.'Ihe unit E' may include amplitude limiters or amplitude amplifiersand/or frequency multipliers.

If, for some reason, grid neutralization of the amplitude modulatortubes G and H of stage C is preferable, the circuit arrangement ofFigure 5 may be used.

In Figure 5 the source of oscillations A is coupled by way of blockingcondensers I and 3 to points on the inductance 40 of the grid tankcircuit X. This tank circuit X is tuned tothe desired frequency byvariable capacity 4|, and the natural impedance of this tuned circuit Xto the oscillations from A is such as to match the low impedance outputof A to the high impedance of the input electrodes of tubes G and H.'Ihe high frequency oscillations from tank circuit X are applied inphase opposition to the control electrodes 2 and 4 of tubes G and H. Thehigh frequency oscillations repeated or multiplied in tubes G and H arefed to tank circuits M and N, However, in this arrangement, since thehigh frequency oscillations are applied in phase opposition'to thecontrol electrodes and not cophasally, as in the prior arrangement,reversal of the energy in one of the amplitude modulators G and H mustbe 'accom-Y plished in order to properly combine the energies ledthrough the phase shifting means L and Q to the grid electrode S of tubeV. This is accomplished by reversing the coupling of one of the tankcircuits M and N with its tubeG or H.

In Figure 5 the coupling between the tank circuit N and tube H isreversed. In other words, the output circuits of these tubes are, in amanner, connected in push-pull so that the energies therein are alike inphase. The phase shifting circuits L and Q are tapped to points on theinductances Il and II' such that the energy drawn from the tank circuitsM and N isY in phase and is fed to the control grid S` in phase exceptfor the phase shift accomplished by the phaser shiftingv elements L andQ; In. this arrangement the grid to anode capacity of the tubes G and His neutralized or compensated by connecting the anode 6 of tube G to thecontrol electrode 4 of tube H andthe anode 8 of tube H to the controlelectrode 2 of tube G by way of neutralizing condensers NC and NC, asshown. Biasing potential for the control electrodes 2 and 4 of tubes Gand H is supplied by way of a lead 34 connecting a point onpotentiometer P1 to the midpoint of inductance 40, which has itsterminals conductively connectedto the control electrodes 2 and 4. Thearrangement of Figure 5 isotherwise the same as the arrangement ofFigure 4.

It will be noted, however, that in Figures 4 and 5 the inductance I4 ofstage D has been replaced by a resistance i4. It will be understood thateither an inductance or a resistance may be used, but it is preferableto use resistance at this point.

In operation the arrangement of Figure 5 operates substantially the sameas the arrangement of Figure 4. However, since there has been a shift inphase of the high frequency oscillations applied to the controlelectrode 4 with respect to the phase of the high frequency oscillationsapplied to the same control electrode in Figure 4, there must be asecond reversal in phase of the energy accomplished before the energy isapplied to the phase shifting elements L and Q and from said elements tothe control grid S of modulator tube V. This is accomplished, asindicated above, by reversing the connection between the anode electrode8 of tube H and the tank circuit N, as shown. 'I'his brings amplifiedand'amplitude modulated energies in the tank circuit in phase. Theamplified and amplitude modulated and/or frequency multiplied energies.

in the tank circuits M and N are fed by way of phase shifting elements Land Q to the modulator tube, as in the prior arrangements. Thismodulation is accomplished in the tube V in the arrangement of Figure 5and the phase modulated and amplitude modulated energy in the tankcircuit R is fed by way of unit E, which may include all of the elementsincluded in the like unit in the prior gures, to the load circuit F.

In the operation of the arrangements shown in Figures l to 5 inclusivethe tank circuits M and N should be tuned alike, that is, to the-samefrequency, whether they are tuned to a fundamental or to a harmonic. Insome cases it is suggested that a slight amount of mutual inductivecoupling between the two circuits M and N be maintained in the properdirection to aid in keeping the two modulator tubes G and H in step. Insome cases this should improve the operation of the transmitter.Moreover, it will be understood that the phase shifting elements L and Qmay take the form of inductances and capacities, or any combinationthereof, or may be replaced by transmission lines of the proper length.These lines may be artificial lines and may include tuning means. Allthat is necessary is that the desired amount of phase shift isintroduced into the amplitude modulator carrier energy reaching the tubeV.

Moreover, it will be understood that tubes of any type known may be usedto replace the tubes used in the circuits included above, which areintended to be illustrative of the invention and are not intended tolimit the invention in any manner except as limited in the claimsappended hereto.

When the tubes G and H are used as frequency multipliers as Well asamplitude modulators, feed back coupling in these circuits may beresorted to to enhance the frequency multiplying effect. 'This may beaccomplished in the arrangements illustrated in Figures 4 and 5 byover-neutralizing the circuits by means of the neutralizing condensersNC and NC. That is, the coupling between the input and output circuitsof tubes G and I-I may be increased by these condensers sulficiently toinsure the desired amount of regeneration.y

Having thus described my invention and the operation thereof, what Iclaim is:

1. Signalling means comprising, a source of oscillations, a modulatortube, a pair of electron discharge tubes having parallel input circuitsconnected to said source of oscillations means for varying theimpedances of said pair of tubes in phase opposition at signalfrequency, and output circuits connected through separate phase shiftingmeans of different character to the input electrode of said modulatortube.

2. Signalling means comprising, a source of substantially constantfrequency oscillations, a thermionic modulator tube, a pair ofthermionic relay tubes having symmetrical input circuits and separateanode circuits, means for applying energy from said source to the inputcircuits of said pair of tubes in phase, and phase shifting means havingdifferent characteristics connecting each of said anode circuits to thecontrol electrode of said modulator tube.

3. Modulating means comprising, a pair of electron discharge repeatertubes each having input and output electrodes, carrier frequencyenergizing circuits connected with the input electrodes of said repeatertubes, a separate tuned tank circuit connected to the output electrodesof each` of said tubes, means connected with said tubes for varying theinternal impedance of said tubes in phase opposition at signalfrequency, a modulator tube having an input electrode, and reactivecircuits of different character connecting the input electrode of saidmodulator tube to each of said tank circuits.

4. A phase modulating means comprising, a pair of thermionic tubeshaving input circuits energized by a carrier frequency Wave and separateanode tank circuits, a modulator tube, phase changing means forconnecting a point on each of said tank circuits to the controlelectrode of said modulator tube to excite the same by energy in phasedisplaced relation from said tank circuits, and a source of modulatingvoltages connecting the control electrodes of said pair of tubes inphase opposition.

5. Phase modulation means comprising, a pair of thermionic tubes of thescreen grid type having input circuits energized by a carrier frequencyWave and separate anode tank circuits, a modulator tube, phase changingmeans for connecting a point on each of said tank circuits to thecontrol electrode of said modulator tube to excite the same by energy inphase displaced relation from said tank circuits, and a source ofmodulating voltages connecting the screen grid electrodes of said pairof tubes in phase opposition.

6. Phase modulating means comprising, a pair of thermionic tubes havinginput circuits energized by a carrier frequency Wave and separate anodetank circuits, a modulator tube, phase changing means for connecting apoint on each of said tank circuits to the control electrodeof saidmodulator tube to excite thel same by energy in jphase displacedrelation from said tank circuits, and a source of modulating voltagesconnected to the anode' electrodes of said pair ofv tubes to vary thepotential of said anodes in phase opposition.

7. 'Iransmitting means comprising a source of oscillations, a pair ofthermionic tubes, means for connecting said source in phase to thecontrol electrodes of said tubes, a separate tank circuit connected tothe anode of each of said tubes, a source of modulating potentials,means for impressing the modulating potentials in phase pposition on theimpedances of said tubes, a modulator tube, and separate phase shiftingmeans connecting the control electrode of said modulator tube to eachtank circuit.

8. Means for relaying and phase modulating high frequency energycomprising, a pair of electron discharge tubes having their inputelectrodes energized in phase by Wave energy of carrier frequency, a`modulator tube, phase retarding means for applying energy from theanode of one of said pair of tubes to the control electrode of saidmodulator tube, phase advancing means for applying energy from the anodeof the other of saidpair of tubes to the same control electrode of saidmodulator tube, and means for impressing modulating potentials in phaseopposition on the internal impedances of said pair of tubes.

9. In a phase modulator, a pair of electron discharge tubes, means forenergizing the control electrodes of said tubes substantially cophasallyby wave energy of carrier frequency,

Separate tank circuits connected With the anodesl of said tubes, meansfor impressing modulating potentials on the internal impedances of saidtubes, a modulator tube, and separate phase sluiting reactances ofdifferent character for impressing energy from said tank circuits inphasen displaced relation on the control electrode of said modulatortube.

10. Signalling means comprising, a source of high frequencyoscillations, a pair of thermionic tubes, means for connecting thecontrol elec-,-

trodes of said tubes to said source so that oscillations therefromappear on said control electrodes in phase, a separate tank circuitcom'- prising a capacity and a tuned inductance connected With theoutput electrodes of each of said. tubes, a work circuit, a modulatortube having its output electrodes coupled to said work circuit, phaseadvancing means connecting one of said tank circuits to the inputelectrodes of said modulator tube,'phase retarding means connecting theother of said tank circuits to the input electrode of said modulatortube, a source of signal voltages, and means connected between saidsource of signal voltages and said pair of tubes forV varying theconductivity of said tubes in phase opposition at signal frequency.

11. The method of signalling Which comprises the steps of, generating aconstant frequency carrier Wave, producing potentials of modulatingfrequency, varying the amplitude of the carrier oscillations inaccordance with Variations in amplitude of the modulating potentials,shifting the phase of the amplitude modulated carrier Wave beforetransmission into a utilizing circuit at a rate dependent upon thevariation in amplitude of the carrier, the shift in phase producing acarrier energy, an undesired and desired side band energy, andcontrolling the amount of undesired side band energy by controlling theam- Y plitude of the modulatingpotentials used to cause nation 'with aconstant frequency generator `of a pair of tubes having input electrodessymmetrically connected Vto said generator, a source Yof modulatingpotentials connected to said input electrodes, .and a combining tubeconnected through separate phase shifting elements one of`whichis-capacitive, the other of which is inductive to the anodes of`said tubes.

13. Ina signalling system, a source of oscillations, a combining tube, apair of like electron discharge Ltubes having input circuitssymmetrically connected to said source of oscillations and outputcircuits one of which is connected through van -inductance and theVother through a condenser to said combining tube, means associatedlWith said Vpair of tubes for preventing reaction lbetween the input andoutput circuits thereof, and means for applying Ymodulating potentialsYto .like electrodes of saidV pair of tubes.

14. A phase modulator comprising, a pair of Ylike electron dischargetubes, means for energizing `the .control electrodes of said tubes co-`phasally by wave energy, a separate tank circuit -.connected with theanodes of each of said tubes,

Ymeans for yimpressing Vmodulating potentials on Athe internal`impedance of said tubes, a combining tube, a phase shifting inductanceand a phase shifting condenser for separately impressing energy kfromsaid tank circuits on the control electrode of said combining tube, andmeans for preventing the wave energy appearing in the tank circuits ofsaid pair of tubes from react- Ying .on the Wave energy applied to thecontrol electrodesof said pairvof tubes.

15. The combination of a source of high irequency oscillations, and asource of signalling Vpotentials of means for modulating the amplitude`of the lhigh frequency oscillations in accordance with signals, saidmeans having an input and an output, a circuit connecting said means toksaid source of signaling potentials, a second circuit connecting saidinput with said source of high frequency oscillations, additional meanscoupled to theoutput of said amplitude modulating means for changing theamplitude modulated oscillations into phase modulated oscillations, and4meansconnected with said amplitude modulating vmeans for preventingkthe .oscillations applied therefrom to said additional means fromaffect- `ing the oscillations applied from said source of `highfrequency oscillations to the input of said amplitude modulating means.

16. In a signalling system'comprising, a source of oscillations, acombining tube having input electrodes, a pair of electron dischargedevices operating as frequency multipliers having input circuitssymmetrically connected to said source of oscillations, said pair ofdischarge devices each having a separate output circuit, a reactanceconnecting one of said output circuits to the input electrodes of saidcombining tube, and a second reactance of different character connectingthe other of said output circuits to said input electrodes.

17. Signaling means comprising, a pair of thermionic tubes each havingan anode, a cathode and a control electrode, a source of carrier Waves,circuits connecting said carrier wave source to the control electrodesand cathodesV of each of said tubes, a separate tank circuit connectedbetween the anode and cathode of each of said tubes, reactances in eachof said tank circuits `rier waves, a source .of lmodulating potentials,

a circuit connecting said source of modulating potentials in phaseopposition to like electrodes in said tubes, .a combining tube having acathode and a control grid, `an impedance connected between the cathodeand control grid of said combining tube and phase shifting reactances ofdifferent character connecting each of said Atank circuits to thecontrolgrid of said combining tube.

18. The. combination with a constant frequency generator of apair ofthermionic tubes having input-electrodes connected to said generator,said tubes also having output electrodes, a thermonic modulator tubehaving an input electrode connected through separate phase shiftingelements to the output electrodes of said iirst named tubes and a sourceof modulating potentials connected with like electrodes in said pair oftubes for varying the internal impedance of said tubes in phaseopposition at signal frequency.

19. Transmitting means comprising, a source of oscillations, a pair ofthermionic tubes, means for connecting said source of oscillations inphase opposition to the control electrodes of said tubes, va separatetank circuit connected to the anode of each of said tubes, a source ofmodulating potentials, means for impressing the modulating potentials inphase opposition on the internal impedance of each of said tubes, acombining tube, a positive phase shifting reactance connecting thecontrol electrode of said combining tube to one of said tank circuits,and a negative phase shifting reactance connecting the control electrodeof said combining tube to the other of said tank circuits.

20. Means for relaying and phase modulating carrier frequency energycomprising, a pair of thermionic tubes having their input electrodesenergized in phase opposition by a carrier frequency Wave, a thermionicmodulator tube, reactive means for applying energy from the anode of oneof said tubes to a control electrode in said modulator tube, means forapplying energy from the anode of the other of said tubes to a controlelectrode in said modulator tube, means for reversingk the phase of theenergy applied by one of said means, and means for impressing modulatingpotentials in phase opposition on the internal impedances of said pairof tubes. y

21. Transmitting means comprising, a source of oscillations, a pair ofthermionic tubes, circuits connecting said source of oscillations inphase opposition to the control electrodes of said tubes, a separatetank circuit, connected to the anode Vof each of said tubes, there beingappreciable coupling between said tank circuits, means for tuningv saidtank circuits to a frequency which is a harmonic of the frequency ofsaid source, a source of modulating potentials, means for impressing themodulating potentials in phase opposition on the anode electrodes ofsaid tubes, a modulator tube, and separate phase shifting meansconnecting the control electrode of said modulator tube to each tankcircuit.

22. Signaling means comprising, a pair of electron discharge tubeshaving symmetrical input circuits and symmetrical grid neutralizationcircuits, a separate tank circuit connected `with the anode Yof each ofsaid tubes, one of said tank circuits being `reversed as to its voltagecharacteristicsv with `respect to the other Atank circuit, means forapplying high frequency oscillationsA in phase opposition Yto said inputcircuits, means for varying oppostely the impedances of said tubes atsignal frequency, a

`utilization circuit, and separate reactances of different characterconnecting said tank circuits to said utilization circuit.

23Signaling means comprising, a source of constant frequencyoscillations, a thermionic modulator tube, a pair of thermionicfrequency multiplier and amplifier tubes having .a tuned input circuit,a separate anode circuit connected to each tube of said pair, a circuitfor applying energy from said source of constant frequency oscillationsto said input circuit and to said pair of tubes in phase opposition,means coupling the input circuit and anode circuits of said pair oftubes, means for tuning the anode circuits of said tubes `to a frequencywhich is a multiple of the frequency of said oscillations, means forvarying the internal impedances of said pair of tubes oppositely atsignal frequency, phase shifting means of different character connectingeach of said anode circuits to the control electrode of said vmodulatortube, and a resistance connected between the control electrode andcathode of said modulator tube.

24. Phase modulating means comprising, a pair of thermionic amplifiersand frequency multipliers of the triode type, a tuned tank circuitconnected with the input electrodes of said arnplifiers and frequencymultipliers, means for energizing said tank circuit by wave energy ofcarrier frequency, an output circuit connected to each amplifier andfrequency multiplier, means for tuning the output circuit of each ofsaid amplifiers and frequency multipliers to a harmonic of theenergizing frequency, means for insuring controlled regeneration in eachof said tubes including a variable capacity connecting an outputelectrode of each of said tubes to an input electrode of the other ofsaid tubes, means for varying the internal impedance of said tubes inphase opposition at signal frequency, a thermionic modulator tube havinga resistance connected between its input electrodes, and phase shiftingmeans for connecting the input electrodes of said modulator tube to eachof said output circuits.

25. Modulating means comprising, a pair of thermionic tubes having inputelectrodes and out .put electrodes, a tuned tank circuit connected tothe input electrodes of said tubes, separate tank circuits connected tothe output electrodes of said tubes, capactive means for tuning saidseparate tank circuits to a harmonic of the frequency to which the inputcircuit is tuned, means for applying high frequency-oscillations to saidinput circuit, a capacity connected between the output electrode of eachof said tubes and the input electrode of the other of said tubes toinsure regeneration in said tubes, a circuit for varying the impedancesof said tubes at signal frequency, and a phase modulator tube having itsinput electrode connected through phase shifting elements to said tankcircuits.

26. In a phase modulation system, a Source of oscillations of carrierwave frequency, an electron discharge tube, a pair of similar tubeslhaving input circuits connected to said source of carrier frequencyoscillations, output circuits connected with each of the tubes of saidpair of similar tubes, a phase shifting coil connecting one of saidoutput circuits to the input electrode of said rst named tube, a phaseshifting condenser connecting the other of said output circuits to theinput electrode of said rst named tube, and circuits for applyingmodulating potentials in phase tentials, means for modulating theamplitude of :f5

the oscillations generated in accordance with said signal potentialscomprising a pair of differential amplitude modulator tubes connected attheir inputs with the output of said generator, said modulator tubesalso acting as frequency multipliers .1'0

and being connected to said source of potentials, and means forconverting the resultant energy into phase modulated oscillationscomprising an additional tube having its input electrodes connectedthrough phase shifting elements to the '15 output of said amplitudemodulator and frequency multiplier tubes, and an amplifier connected atits input With the output of said additionai tube.

28. The combination with a master oscillator,r20

a pair of tank circuits, a source of signal potentials, means formodulating the amplitude of the oscillations produced by said oscillatorin accordance with signals from said source comprising a pair ofamplitude modulator tubes connected at 25 their inputs to saidoscillator and at their outputs to said tank circuits, circuitsconnecting said source of signal potentials to like electrodes in saidmodulator tubes, and means for converting the energy in the output ofsaid tubes into phase modulated oscillations comprising an additionalcombining tube having a control electrode connected to each of said tankcircuits, and phase shifting means of different character in theconnections between said control electrode and said tankv circuits.

29. In a signaling means the combination of a source of high frequencyoscillations, a source of signal potentials, a radiating circuit, meansfor modulating the amplitude of the oscillations of said high frequencysource in accordance with signals from said source of signal potentialscomprising an amplitude modulator and frequency multiplier connected atits input to said source of high frequency oscillations, circuitsconnecting said amplitude modulator and frequency multiplier to saidsource of signal potentials, and means for converting the resultantenergy into phase modulations, said means having -an input and an outputand being connected at its input through phase shifting elements to saidamplitude modulator and at its output to said vradiating circuit.

30. The combination of a constant frequency oscillation generator, asource of modulating potentials, means for modulating the oscillationsgenerated in accordance with potentials from said source of modulatingpotentials comprising a pair of amplitude modulator tubes, said tubesalso acting as frequency multipliers, circuits con- 50 ecting the inputelectrodes of said tubes to the output of said generator and connectingelectrodes in said tubes to said source of signal potentials, and meansfor converting the resultant energy into phase modulated oscillationscomprising an additional tube, phase shifting reactances of differentcharacter connecting the input electrodes of said additional tube to theoutputs of each of said pair of tubes, an amplifier and frequencymultiplier connected at its input '10 with the output of said additionaltube, and means for neutralizing the internal capacity betweenelectrodes in the amplitudey modulator tubes.

31. The method of signalling by means of high frequency oscillations andsignal potentialsV which includes the steps of dividing the highfrequency oscillatory energy into two portions, multiplying thefrequency of the high frequency oscillations in each portion andsimultaneously varying the amplitude of said portions in phaseopposition in accordance with the signal potentials, shifting the phaseof the oscillatory energy in each portion, and combining the resultantenergies.

32. The method of signaling by means of carrier frequency oscillatoryenergy and signal p0- tentials which includes the steps of separatingsaid oscillatory energy of carrier frequency into tw-o portions, thephases of the oscillatory energies of said portions being displacedsubstantially 180, differentially amplitude modulating the oscillatoryenergy in said portions at signal frequency, relatively shifting thephase of the differentially amplitude modulated oscillatory energy insaid portions, and combining the energies in the portions to pr-oduce aresultant the phase of which is determined by the relative amounts ofsaid portions combined.

33. Transmitting means comprising a source of oscillations, a pair ofthermionic tubes, circuits connecting said source of oscillations to thecontrol electrodes of said tubes, separate tank circuits connected tothe anode of each of said tubes, there being an appreciable couplingbetween said tank circuits, a source of modulating potentials, means forimpressing the modulating potentials in phase opposition on likeelectrodes of said tubes, an additional tube, and separate reactivemeans of different character connecting the control electrode of saidadditional tube to each tank circuit.

34. In a phase modulation system, a pair of electron discharge tubeseach having input and output electrodes, carrier wave frequencyenergizing circuits connected with the input electrodes of said tubes, aseparate tuned tank circuit connected to the output electrodes of eachof said tubes, means connected with said tubes for varying the internalimpedance of said tube in phase opposition at signal frequency, acombining tube having an input electrode, a phase shifting inductanceconnecting the input electrode of said combining tube to one of saidtank circuits, and a phase shifting condenser connecting the inputelectrode of said combining tube to the other of said tank circuits.

35. In a signalling system, means for differentially amplitudemodulating two portions of oscillatory energy of like frequency inaccordance with signals, means for simultaneously increasing thefrequency of the oscillatory energy of each portion like amounts, meansfor relatively phase shifting the energy of said two differentialyamplitude modulated portions, and means for combining the resultants toproduce a component the phase of which varies at signal frequency.

36. A method of impressing phase changes at signal frequency or waveenergy comprising, dividing the energy from a source of wave energy intotwo branches, differentially modifying the amplitudes of the energy inthe branches in accordance with signals, then subjecting the energy inone branch to a leading power factor and subjecting the energy in theother branch to a lagging power factor, then combining the energy fromthe two branches so that the combined wave is bf substantially constantamplitude with a varying phase.

37. In an amplifier for modulating high frequency waves, a radiotransmitter, two parallel branch circuits to which high frequency waveenergy is fed by the transmitter, means for introducing a signalcomponent on the high frequency energy in each branch, a capacitativereactance in the output of one branch and an inductive reactance in theoutput of the other branch, and` means for coupling said capacitativeand inductive reactances whereby there is generated an output wave ofsubstantially constant amplitude whose longitudinal dimensions varyabout a medial point in accordance with the signal component.

38. Means for impressing phase modulations at signal frequency oncarrier frequency oscillations including, a pair of thermionic tubeshaving their input electrodes connected ln circuits for impressing theoscillations to be modulated on the control grids of said tubes, theimpressed oscillations being of like phase, means for varying theimpedances of said tubes in phase opposition at signal frequency, andseparate circuits connected with the output electrodes of said tubes forrelatively shifting the phase of the oscillations repeated in saidtubes.

39. The method of producing carrier wave energy modulated in phase atsignal frequency which includes the steps of, separately modulating theamplitude of a plurality of carrier wave oscillations, of like phase andfrequency, in opposite sense at signal frequency, relatively shiftingthe phases of the amplitude modulated 'carrier wave oscillations of likefrequency, and combining the resultant energy to produce wave energymodulated in phase at signal frequency.

40. In a system for producing oscillatory energy modulated in phase inaccordance with signals, a source of oscillatory energy of carrier wavefrequency, an output circuit, two parallel branches each having an inputto which oscillatory energy is fed from said source of oscillatoryenergy, means for modulating the amplitude of the oscillatory energy ineac`h branch at signal frequency, a capacitive reactance coupling onebranch to said output circuit, an inductive reactance coupling the otherbranch to said other output circuit and means associated with saidbranches for preventing oscillatory energy therein and in said outputcircuit from reacting on said source of oscillatory energy.

41. In a phase modulating system, an output circuit, a source 'ofmodulating potentials, a source of high frequency oscillations, a pairof thermioni'c tubes having separate anode circuits coupled to saidoutput circuit, and circuits connecting the electrodes of said tubes tosaid sources to apply carrier frequency waves to said tubes and phaseopopsed modulating potentials to the impedances between like electrodesof said tubes, whereby the carrier frequency waves in said tubes aredifferentially modulated in amplitude and phase shifting means in theanode circuits of said tubes for producing relative phase shifts of thedifferentially amplitude modulated waves in said anode circuits.

GEORGE L. USSELMAN.

